Radar sensors for recording the nearby motor vehicle environment (SRR, short range radar sensors) may be provided for functions such as backup aid, parking assistance, parking gap measurement, blind spot monitoring, slow bumper to bumper driving or precrash detection.
Besides the information on the distance of relevant objects (other vehicles, traffic lane limitations or parking gap limitations, pedestrians, etc.) information on their angular position relative to the vehicle may also be important for judging the relevance of detected objects for whatever the vehicle is doing. In this regard, the angular direction of objects may be calculated via so-called trilateration. In this method, the distance data of several neighboring sensors are used in order also to determine the angular deviation of targets, using simple trigonometric conversions. With this method more and more sensors may be required at a certain distance apart, even to ascertain the position of only one target. Then too, these sensors in each case have to detect the same target, so as not to obtain faulty estimations.
International Published Patent Application No. WO 00/49423 describes a monopulse phase array antenna system, which has transmitting and receiving modules which are controlled by a beam swivel control device. From the received signals from the various antenna elements, composite signals and angular differential signals are derived. Each of the transmitting and receiving modules is furnished with two 180° phase shifters, in order to determine the angular differential signals. For the independent tracking in the azimuth and elevation direction, one may evaluate a composite signal and two differential signals.
M. Skolnik, Introduction to Radar Systems, second edition, McGraw Hill Book Company, 1980, pages 160 and 161, discuss that one may obtain the angular information of a target object from two mutually overlapping antenna beam characteristics.